1. Technical Field of the Invention
The present invention relates to a data reproduction apparatus for a disk medium reproducing digital data from a digital disk, such as CD, CD-ROM, or the like, on which the digital data have been recorded along a spiral track, and more particularly relates to reading of subcode data indicating a position or attributes of a data body.
2. Background of the Invention
Conventionally, on a CD, a CD-ROM disk, or the like, used as a bulk data recording medium, data signals have been recorded by a CLV (constant linear velocity) system. Further, in this disk, a data body and subcode data indicating the position or attributes of the data body have been recorded along a spiral track.
In a CD-ROM disk, generally, one data block (sector) is constituted by 98 data frames. Each data frame has 24 bytes of data and 8 bytes of them are distributed for subcodes (channel P to W). In channel Q of each subcode (sub Q code), the value of the absolute time of the data block is recorded. In the sub Q code in a read-in region (innermost region of the disk), information concerning the arrangement of a program region and a read-out region (outermost region of the disk-) is recorded as search information. This information is called TOC (table of contents), and in this information, the absolute time of the head portion of each track in the program region, the control information of each track, the first and last track numbers of the program region, and the starting absolute time of the program region are recorded. The sub Q codes can be extracted from the subcodes in accordance with a subcode synchronizing signal having 75 Hz of frequency.
The subcode is necessary for grasping the current position of a pickup on a disk at the time of seeking, and for obtaining the number of tracks between the current position and a target position which is the destination of movement of the pickup, and the numerical value thereof must be arcuate. A servo mechanism is relatively stable at the time of ordinary reproducing. However, the timing when the subcode is read in seeking time is just after track jump so that the servo mechanism is unstable, and sometimes there is a fear that an erroneous subcode data may be read. Not only this defect is a fatal hindrance for seeking operation and makes the seeking operation take a long time, but also this defect may cause such an accident that the pickup comes off from the outermost circumference of the data recorded position of a disk.